A small but significant number of pipeline failures occur each year and many in populated regions arise as a result of mechanical damage from external interference. These failures generally occur at the time of damage, but a small number are delayed, with the final failure reportedly taking place following periods of up to 40 years from the original damage. This type of failure is of concern to pipeline operators as they occur without warning. The mechanisms governing time-delayed failures are poorly understood due to the extremely limited experimental data available. A greater understanding of the failure mechanism would help operators to improve their strategies for managing external interference damage. In the event of combined dent and gouge mechanical damage, the model described in this paper provides an approach for the assessment of the time dependent failure modes of the defective pipeline. The model, developed using Matlab code, is capable of investigating a complex load history consisting of constant internal pressure hold periods and cyclic fluctuations and can predict time dependent phenomenon such as pressure reversals sometimes experienced following hydrostatic pressure testing. The approach is based on the BS 7910 material specific Failure Assessment Diagram (FAD) in conjunction with R5 (British Energy) creep procedures. The result is a time dependent FAD which allows the combined influence of time dependent material properties (toughness, strength and cold creep) and loading to be investigated.

This content is only available via PDF.
You do not currently have access to this content.